Guillain-Barré Syndrome (GBS) is rare in infancy, and the diagnosis of atypical forms is difficult in this age range. The main differential diagnoses include congenital neuropathy. Biological and electrophysiological investigations remain important to confirm diagnosis and start treatment quickly. We report the case of an 8-month-old boy who presented with acquired hypotonia due to progressive descending limb paralysis, predominant in the upper limbs, associated with unexplained severe neutropenia. GBS was diagnosed thanks to the association of albuminocytologic dissociation on cerebrospinal fluid and demyelinating sensomotor polyradiculoneuropathy on electroneuromyography. Only one cycle of treatment with intravenous immunoglobulins was sufficient to achieve complete recovery after 1 year. Physicians should know that atypical forms of GBS exist in infants, in order to recognize the syndrome, rule out differential diagnoses, and start treatment as soon as possible. Medical follow-up remains important before and after remission, especially in infants, to identify relapses, which might be the symptom of a genetic neuropathy or a chronic inflammatory disease.